The present invention relates to a fabrication technology of a semiconductor device, more specifically to a semiconductor device having a DRAM-type memory device and a method for fabricating the same.
A DRAM is a semiconductor memory device which can be formed by one transistor and one capacitor. Various structures for DRAMs of higher density and higher integration, and methods for fabricating DRAMs of such structures have been conventionally studied.
Recently in the field of the fabrication of the DRAM-type semiconductor device the competition among makers has become severe, and it is an important subject how to fabricate DRAM-type semiconductor devices of higher integration and higher achievement at low costs.
To this end, the capacitor requires a simpler structure. Structures which are simple and can secure sufficient capacities are studied. One of such structures of the capacitor uses a pillar-shaped conductor as the storage electrode.
A semiconductor device using the pillar-shaped conductor as the storage electrode will be explained with reference to FIG. 52.
On a semiconductor substrate 10 there are formed source/drain diffused layers independent of each other. A gate electrode 18 is formed on the semiconductor substrate 10 between the source/drain diffused layers 20, 22 through a gate oxide film. Thus a memory cell transistor comprising a gate electrode 18, the source/drain diffused layers 20, 22 is formed.
An inter-layer insulation film 24 with a through-hole formed in above the source/drain diffused layer 20 is formed on the semiconductor substrate 10 with the memory cell transistor formed on.
In the through-hole a storage electrode 46 is formed with the bottom connected to the source/drain diffused layer 20 and protruded onto the inter-layer insulation film 24. An opposed electrode 56 is formed on the upper surface and the sidewalls of the storage electrode 46 through a dielectric film 52, and the storage electrode 46, the dielectric film 52 and the opposed electrode 56 constitute a capacitor.
On the semiconductor substrate 10 with the memory cell transistor and the capacitor interconnections 60, 62 are formed trough an inter-layer insulation film 68. The interconnection 60 is connected to the opposed electrode 56, and the interconnection 62 is connected to the semiconductor substrate 10 in a peripheral circuit region.
Thus a DRAM comprising one transistor and 1 capacitor is formed.
As described above, the conventional semiconductor device shown in FIG. 52 has the storage electrode 46 constituting the capacitor in the simple pillar-shaped structure, which can be easily formed by one film forming step and one patterning step. Thus the capacitor forming step can be drastically simplified, and the forming costs can be accordingly lower.
However, in the conventional semiconductor device using the pillar-shaped storage electrode 46 the memory cell region is higher than the peripheral circuit region by a height of the storage electrode 46, which makes it difficult to open a contact hole for connecting the interconnection 62 to a peripheral circuit.
That is, usually a contact hole for connecting the interconnection to the peripheral circuit is formed through the inter-layer insulation film 48 formed on the storage electrode 46 (FIG. 52). However because of a large height difference of the inter-layer insulation film 68 between the memory cell region and the peripheral region, in simultaneously forming the contact hole to be opened on the opposed electrode 56 and the contact hole to be opened in the peripheral region, a sufficient depth of focus cannot be obtained in the contact hole opening step and the metallization step, which required micronized processing precision. Neither of the two contact holes cannot be correctly formed.
To ensure a sufficient depth of focus, the inter-layer insulation film 68 is planarized by, e.g., CMP (chemical mechanical polishing) method. However, the contact hole in the peripheral circuit region has a very high aspect ration, which makes it difficult to open the contact hole. It also makes it difficult to bury the interconnection in the contact-hole (FIG. 53).
To the semiconductor device fabrication process it is important for lower fabrication costs how to decrease lithography steps, and semiconductor structures and methods for fabricating the same which can decrease lithography steps are needed.
Each lithography step needs a pattern layout which considers a alignment allowance. For micronization of the devices, new means which enables the pattern layout to be conducted without considering the alignment allowance is needed.
An object of the present invention is to provide a semiconductor device and a method for fabricating the same which can form a memory cell in a simple structure and by a simple fabrication process, and which are superior in alignment with a process for forming a contact hole in a peripheral circuit region.
The above-descried object is achieved by a semiconductor device including a memory cell region and a peripheral circuit region of a semiconductor substrate, comprising: a transfer transistor formed in the memory cell region; a capacitor connected to one of diffused layers of the transfer transistor and including a storage electrode formed of a first conducting layer, a dielectric film covering a sidewall of the storage electrode and an opposed electrode formed on the dielectric film; a first conducting plug formed of the first conducting layer and connected to the peripheral circuit region of the semiconductor substrate; and a first interconnection electrically connected to the first conducting plug. This structure of the semiconductor device allows the region interconnecting the first interconnection and the semiconductor substrate to be raised by the first conducting plug, which makes it unnecessary to open the contact hole deep enough to reach the semiconductor substrate so as to bury the first interconnection, with the result that the etching step and the interconnection forming step can be simple. Also in forming the interconnection connected to the opposed electrode simultaneously with the first interconnection, because the opposed electrode and the first conducting plug are substantially on the same level, the contact hole and the interconnection can be patterned irrespective of depth of focus. Because the first conducting plug can be formed of the same conducting layer as the storage electrode, the first conducting plug can be formed without making fabrication process complicated.
In the above-described semiconductor device, it is preferable that the storage electrode includes a second conducting layer on a surface thereof contacting the dielectric film. This structure of the semiconductor device makes it possible to maintain an operational speed of the semiconductor device without degrading characteristics of the capacitor. That is, it is preferred that the first conducting plug interconnecting the first interconnection and the semiconductor substrate has smaller resistance value because a resistance value of the first conducting plug influences the operational speed of the semiconductor device. On the other hand, it is required that a storage electrode have good compatibility with a dielectric film, and to this end, because the dielectric film and the first conducting plug are formed of the same material, a material thereof must be selected based on both conditions. However, this structure makes it possible to select a material low resistance as a material of the first conducting plug without considering a material of the storage electrode. Thus, without degrading characteristics of the capacitor, the semiconductor device can retain an operational speed.
In the above-described semiconductor device, it is preferable that a plurality of the storage electrodes are provided, and the opposed electrode is buried between said a plurality of the storage electrodes. This structure of the semiconductor device makes it possible to form the opposed electrode by self-alignment with the storage electrode. A lithography step for patterning the opposed electrode is not necessary.
In the above-described semiconductor device, it is preferable that the semiconductor device further comprises, on a sidewall of the first conducting plug, a first insulation film formed of the same insulation layer as the dielectric film, and a sidewall film formed of the same conducting layer as the opposed electrode.
In the above-described semiconductor device, it is preferable that the first conducting plug is crown-shaped.
In the above-described semiconductor device, it is preferable that a second conducting layer is buried in the crown-shaped first conducting plug.
In the above-described semiconductor device, it is preferable that the semiconductor device further comprises a dummy electrode formed of the first conducting layer and insulated from the semiconductor substrate; and a second interconnection connected to the opposed electrode, wherein the opposed electrode is extended on a sidewall of the dummy electrode or on the dummy electrode, and the second interconnection is connected to the opposed electrode at a region where the dummy electrode is provided. This structure of the semiconductor device facilitates connection of the second interconnection to the opposed electrode without short-circuiting with the storage electrode.
In the above-described semiconductor device, it is preferable that the first interconnection is a buried interconnection buried in a second insulation film formed on the first conducting plug. The first interconnection can be a buried interconnection.
In the above-described semiconductor device, it is preferable that a cavity is formed in a peripheral part of the first conducting plug. This structure of the semiconductor device makes it possible to reduce parasitic capacitance between the interconnections.
In the above-described semiconductor device, it is preferable that the semiconductor device further comprises: a second conducting plug connected to the other diffused layer of the transfer transistor and formed of the first conducting layer; and a bit line electrically connected to the second conducting plug. This structure allows the second conducting plug to be used for the connection between the second conducting plug and the transfer transistor.
In the above-described semiconductor device, it is preferable that the semiconductor device further comprises: an annular dummy electrode provided around the memory cell region and surrounding the same.
In the above-described semiconductor device, it is preferable that the annular dummy electrode is formed of the first conducting layer.
In the above-described semiconductor device, it is preferable that the semiconductor device further comprises: a third insulation film selectively covering a surface of the opposed electrode; and a third interconnection arranged on the capacitor, the third interconnection being insulated from the opposed electrode by the third insulation film. This structure of the semiconductor device keeps the interconnection of the capacitor from connecting to the opposed electrode, which permits the interconnection for connecting to the peripheral circuit region can be extended on the memory cell region. Thus, the layout of the interconnection of a peripheral circuit can have high freedom degree, and accordingly the semiconductor device can have improved integration.
The above-described object can be also achieved by a method for fabricating a semiconductor device comprising: a storage electrode forming step of forming a plurality of storage electrodes on a base substrate; a dielectric film forming step of forming a dielectric film covering said a plurality of storage electrodes; and an opposed electrode forming step of depositing and etching back a first conducting film on the base substrate with the dielectric film formed on to form an opposed electrode filled between said a plurality of storage electrodes covered with the dielectric film and formed of the first conducting film. This fabrication of the semiconductor device makes it possible to form the opposed electrode by self-alignment with the storage electrode, which allows a lithography step required to form an opposed electrode by the conventional semiconductor device fabrication method to be omitted.
The above-described object can be also achieved by a method for fabricating a semiconductor device comprising: a storage electrode forming step of forming a plurality of storage electrodes in a first region of a base substrate and forming a first pillar-shaped conductor formed of the same conducting layer as the storage electrodes in a second region of the base substrate; a dielectric film forming step of forming a dielectric film covering said a plurality of storage electrodes; an opposed electrode forming step of depositing and etching back a first conducting film on the base substrate with the dielectric film formed on to form an opposed electrode filled between said a plurality of storage electrodes covered with the dielectric film and formed of the first conducting film; and an interconnection forming step of forming a first interconnection on the first pillar-shaped conductor and connected to the base substrate in the second region through the first pillar-shaped conductor. This fabrication of the semiconductor device allows the region interconnecting the first interconnection and the semiconductor substrate to be raised by the first pillar-shaped conductor. Because the pillar-shaped conductor can be formed of the same conducting layer as the storage electrode, the pillar-shaped conductor can be formed without making fabrication process complicated. Because the opposed electrode can be formed by self-alignment with the storage electrode, a lithography step for patterning the opposed electrode is not necessary.
In the above-described method for fabricating a semiconductor device, it is preferable that in the opposed electrode forming step, a sidewall film formed of the first conducting film and formed on a sidewall of the first pillar-shaped conductor is further formed.
In the above-described method for fabricating a semiconductor device, it is preferable that the method further comprises after the opposed electrode forming step: a first insulation film forming step of depositing a first insulation film; and a first insulation film removing step of removing the first insulation film until top surfaces of the storage electrodes and of the pillar-shaped conductor are exposed. This fabrication of the semiconductor device exposes by self-alignment the first pillar-shaped conductor on the surface of the first insulation film, which makes it unnecessary to open by lithography a new contact hole which reaches the first pillar-shaped conductor, and makes it possible to form the interconnection connected to the base substrate without disalignment.
In the above-described method for fabricating a semiconductor device, it is preferable that in the storage electrode forming step, the storage electrodes and the first pillar-shaped conductor having the top surfaces covered with a cap film are formed; and in the first insulation film removing step, the first insulation film is removed until a top surface of the cap film is exposed. This fabrication exposes self-alignment the opposed electrode on the surface of the first insulation film, which makes it possible to for the interconnection connected to the base substrate without forming a new contact hole.
In the method for fabricating a semiconductor device, it is preferable that the method further comprises after the first insulation film removing step: a cap film removing step of removing the cap film on the first pillar-shaped conductor to expose the first pillar-shaped conductor. This fabrication of the semiconductor device makes it possible to form by self-alignment the contact hole exposing the first pillar-shaped conductor. The cap film is formed of an insulating material, and the cap film in the memory cell-region is selectively left on, whereby the opposed electrode alone can be exposed in the memory cell region. Thus, the interconnection formed in the memory cell region can be connected only to the opposed electrode without interposing the inter-layer insulation film.
In the above-described method for fabricating a semiconductor device, it is preferable that the method further comprises after the first insulation film removing step: a second insulation film forming step of depositing a second insulation film; and an opening forming step of forming a first opening opened on the first pillar-shaped conductor in the second insulation film. This fabrication of the semiconductor device makes it also possible that the first interconnection is connected to the first pillar-shaped conductor through the first opening formed in the second insulation film.
In the above-described method for fabricating a semiconductor device, it is preferable that in the storage electrode forming step, a second pillar-shaped conductor which is not electrically connected to the base substrate and spaced from the storage electrodes by a prescribed interval, and are formed of the same conducting layer as the first pillar-shaped conductor is formed in a third region adjacent to the first region; and in the opening forming step, a second opening formed in the second insulation film on the opposed electrode near the second pillar-shaped conductor. This fabrication of the semiconductor device can prevents the second opening formed in the second insulation film from extending on the storage electrode. Thus, the lithography step for forming the second opening can be simplified.
In the above-described method for fabricating a semiconductor device, it is preferable that the method further comprises after the first insulation film removing step: a second insulation film forming step of depositing a second insulation film; and an opening forming step of forming a second opening opened on the opposed electrodes in the second insulation film.
In the above-described method for fabricating a semiconductor device, it is preferable that the method further comprises after the first insulation film removing step: a second insulation film forming step of chemically or thermally treating a surface of the opposed electrode to form a second insulation film on the surface of the opposed electrode. This fabrication of the semiconductor device makes it possible the interconnection can be formed on the memory cell region, insulated from the opposed electrode.
In the method for fabricating a semiconductor device, it is preferable that in the storage electrode forming step, a second pillar-shaped conductor formed of the same conducting layer as the first pillar-shaped conductor, and spaced from the storage electrodes at a prescribed interval and not connected electrically to the base substrate is further formed in a third region adjacent to the first region; and which further comprises after the second insulation film forming step, an opening forming step of forming a second opening formed in the second insulation film on the opposed electrode near the second pillar-shaped conductor. This fabrication of the semiconductor device can prevent the second opening for forming the insulation film from extending on the storage electrode. Thus, the lithography step for forming the second opening can be made simple.
In the method for fabricating the semiconductor device, it is preferable that the first opening is an interconnection groove for burying an interconnection in the insulation film. The first interconnection is a buried interconnection buried in the second insulation film.
In the method for fabricating the semiconductor device, it is preferable that the method further comprises after the storage electrode forming step: a conducting film forming step of forming a second conducting film on sidewalls of the storage electrodes. Because by providing the second conducting film on the sidewalls of the storage electrode, a material of the storage electrode does not influence characteristics of the dielectric film, the storage electrode can be formed of a material having a desirable low resistance which is suitable for the first pillar-shaped conductor.
The above-described object can be also achieved by a method for fabricating a semiconductor device comprising: a pillar-shaped conductor forming step of forming a pillar-shaped body formed in a first region of a base substrate and formed of a first conducting layer and a second conducting layer laid the latter on the former, and forming a first pillar-shaped conductor connected to a second region of the base substrate and formed of a first conducting layer and a second conducting layer laid the latter on the former; a sidewall film forming step of forming a sidewall film formed of a third conducting film on a sidewall of the pillar-shaped body and the first pillar-shaped conductor; a storage electrode forming step of selectively removing the second conducting film forming the pillar-shaped body and forming a crown-shaped storage electrode of the first conducting film and the sidewall in the first region; a dielectric film forming step of forming a dielectric film for covering the storage electrodes; an opposed electrode forming step of depositing and patterning a fourth conducting film on the base substrate with the dielectric film formed on and forming an opposed electrode covering the storage electrodes through the dielectric film; and an interconnection forming step of forming a first interconnection on the first pillar-shaped conductor and connected to the base substrate in the second region through the first pillar-shaped conductor. This fabrication of the semiconductor device can raise the region interconnecting the first interconnection and the base substrate by the first pillar-shaped conductor, which makes it unnecessary to make the contact hole deep enough to reach the semiconductor substrate to bury the first interconnection. Accordingly the etching step and the interconnection forming step can be simplified. The crown-shaped storage electrode can be formed simultaneously with the formation of the first pillar-shaped conductor, which makes it possible to form the pillar-shaped conductor without complicating fabrication process. By using the crown-shaped capacitor, a height of the storage electrode and the first pillar-shaped conductor can be reduced to about a half, and accordingly the first pillar-shaped conductor can have reduced electric resistance.
The above-described object can be also achieved by a method for fabricating a semiconductor device comprising: a pillar-shaped conductor forming step of depositing and patterning a first conducting film on a base substrate and forming the first conducting film having an opening on a first region of the base substrate and having a first pillar-shaped conductor on a second region of the base substrate; a second conducting film forming step of forming a second conducting film on the first conducting film and the base substrate; a second conducting film removing step of removing the second conducting film, leaving the second conducting film on a inside wall and a bottom surface of the opening and on a sidewall of the first pillar-shaped conductor, and forming a storage electrode extended from the bottom surface of the opening to the inside wall of the opening, and a sidewall film formed on the sidewall of the first pillar-shaped conductor; a first conducting film removing step of removing the first conducting film except the first conducting film formed in the second region; a dielectric film forming step of forming a dielectric film covering a surface of the storage electrode; an opposed electrode forming step of depositing and patterning a fourth conducting film on the base substrate with the dielectric film formed on, and forming an opposed electrode covering the storage electrode through the dielectric film; and an interconnection forming step of forming a first interconnection formed on the first pillar-shaped conductor, and connected to the base substrate in the second region through the first pillar-shaped conductor. This fabrication of the semiconductor device can raise the region interconnecting the first interconnection and the base substrate by the first pillar-shaped conductor, which makes it unnecessary to make the contact hole deep enough to reach the semiconductor substrate to bury the first interconnection. Accordingly the etching step and the interconnection forming step can be simplified. The crown-shaped storage electrode can be formed simultaneously with the formation of the first pillar-shaped conductor, which makes it possible to form the pillar-shaped conductor without complicating fabrication process. By using the crown-shaped capacitor, a height of the storage electrode and the first pillar-shaped conductor can be reduced to about a half, and accordingly the first pillar-shaped conductor can have reduced electric resistance.
In the above-described method for fabricating a semiconductor device, it is preferable in which in the pillar-shaped conductor forming step, the first pillar-shaped conductor having a top surface covered with a cap film is formed; and the method further comprises after the opposed electrode forming step: a first insulation film forming step of depositing a first insulation film; a fist insulation film removing step of removing the first insulation film until a top surface of the cap film is exposed; and a cap film removing step of removing the cap film on the first pillar-shaped conductor to expose the first pillar-shaped conductor. This fabrication of the semiconductor device makes it possible to form by self-alignment the contact hole for exposing the first pillar-shaped conductor.
In the above-described method for fabricating a semiconductor device, it is preferable that in the pillar-shaped conductor forming step, the cap film is formed of a fifth conducting film having substantially the same etching characteristics as the first conducting film, and a mask film to be a mask for processing the second conducting film formed on the fifth conducting film; and in the cap film removing step, the mask film is removed to expose the fifth conducting film on the first pillar-shaped conductor. This fabrication of the semiconductor device makes it possible that even in a case that the second conducting film is formed of a material which is difficult to have a selective ratio with respect to the resist film, the second conducting film can be processed stably to form the storage electrode and the first pillar-shaped conductor. Because the fifth conducting film is formed of a film having substantially the same etching characteristics as the first conducting film, the storage electrode and the first conducting film forming the first pillar-shaped conductor can be processed simultaneously with the removal of the fifth conducting film ont eh storage electrode.
In the above-described method for fabricating a semiconductor device, it is preferable that the method further comprises after the first insulation film removing step: a second insulation film forming step of depositing a second insulation film; and an opening forming step of forming in the second insulation film a first opening formed on the first pillar-shaped conductor, in the cap film removing step, the cap film exposed in the first opening is removed. This fabrication of the semiconductor device makes it possible to connect the first interconnection to the first pillar-shaped conductor through the second insulation film.
In the above-described method for fabricating a semiconductor device, it is preferable that in the pillar-shaped conductor forming step, a second pillar-shaped conductor formed of the same conducting layer as the first pillar-shaped conductor, and spaced from the storage electrode by a prescribed interval and not connected electrically to the base substrate is formed in a third region adjacent to the first region; and in the opening forming step, a second opening opened on the opposed electrode near the second pillar-shaped conductor is formed in the second insulation film. This fabrication of the semiconductor device makes it possible that the second opening for connecting the interconnection to the opposed electrode is opened easily and simultaneously with the first opening.
In the method for fabricating a semiconductor device, it is preferable that the formation of the first opening and the second opening in the opening forming step and the removal of the cap film in the cap film removing step are conducted with one resist pattern as a mask. This fabrication of the semiconductor device makes it possible that the formation of the first opening and the second opening, and the removal of the cap film can be conducted with one resist pattern as a mask. Accordingly the contact hole for exposing the opposed electrode and the first pillar-shaped conductor can be formed without complicating fabrication process.
In the above-described method for fabricating a semiconductor device, it is preferable that in the interconnection forming step, a second interconnection connected to the opposed electrode is further formed.
The above-described object can be also achieved by a method for fabricating a semiconductor device comprising: an insulation film forming step of forming an insulation film on a base substrate; a storage electrode forming step of forming a storage electrode buried in the insulation film and buried in a first opening formed in a first region, and a first pillar-shaped conductor buried in the insulation film and buried in a second opening formed in a second region; an insulation film removing step of selectively removing the insulation film in the first region to expose a sidewall of the storage electrode; a dielectric film forming step of forming a dielectric film for covering a surface of the storage electrode; a opposed electrode forming step of forming an opposed electrode on the surface of the storage electrode through the dielectric film; and an interconnection forming step of forming a first interconnection disposed on the first pillar-shaped conductor and connected to the base substrate in the second region through the first pillar-shaped conductor. The storage electrode and the first pillar-shaped conductor are formed by forming openings in the insulation film having good global flatness and burying the conducting film in the opening, so that the surface flatness of the insulation film can be more improved than in the case that the storage electrode and the first pillar-shaped conductor are formed before forming the insulation film.
In the above-described method for fabricating a semiconductor device, it is preferable that in the storage electrode forming step, an annular dummy electrode disposed around the first region and surrounding the same, and buried in a third opening formed in the insulation film is further formed; and in the insulation film removing step, the insulation film in the first region is selectively removed with the annular dummy electrode as a stopper. As in the case that the insulation film is formed prior to the formation of the storage electrode and the pillar-shaped conductor, a space for burying the opposed electrode can be selectively formed in the insulation film, because the annular dummy electrode is disposed around the first region and surrounding the same.
In the above-described method for fabricating a semiconductor device, it is preferable that in the storage electrode forming step, the first opening, the second opening and the third opening are concurrently formed, and the storage electrode, the first pillar-shaped conductor and the annular dummy electrode are formed of the same conducting layer. The storage electrode, first pillar-shaped conductor and annular dummy electrode can be formed simultaneously so that the fabrication process can be rationalized.
In the above-described method for fabricating a semiconductor device, it is preferable that in the storage electrode forming step, the first opening, the second opening and the third opening are formed at different times, and the storage electrode, the first pillar-shaped conductor and the annular dummy electrode are formed of conducting layers different form each other, whereby the storage electrode and the first pillar-shaped conductor can be formed by different materials each other.
In the above-described method for fabricating a semiconductor device, it is preferable that in the insulation film removing step, the insulation film is removed with a mask member, as a mask, for exposing at least a partial region of the insulation film in the first region, whereby the alignment precision of the lithography step can made rough. Thus, the lithography step can be simplified.
In the above-described method for fabricating a semiconductor device, it is preferable that in the insulation film removing step, the insulation film is removed by wet etching, in which etching isotropically advances, whereby all the insulation film in the first region can be selectively etched by using the mask for exposing at least a partial region of the insulation film in the first region.
In the above-described method for fabricating a semiconductor device, it is preferable that the method further comprising after the storage electrode forming step: a first conducting film replacing step of replacing the first conducting film forming the first pillar-shaped conductor by a third conducting film of lower resistance value by the time when the processing arrives at the interconnection forming step. This fabrication of the semiconductor device makes it possible that the first pillar-shaped conductor is selectively replaced by a low-resistance material in a later step even in a case that the storage electrode and the first pillar-shaped conductor are formed of a high-resistance material having good compatibility with the dielectric film.
In the above-described method for fabricating a semiconductor device, it is preferable that in the first conducting film replacing step, the first conducting film of polycrystalline silicon film is exposed to WF6 gas to replace the first conducting film with a third conducting film formed of tungsten film.
In the above-described method for fabricating a semiconductor device, it is preferable that in the interconnection forming step, the second interconnection connected to the opposed electrode is further formed. This fabrication of the semiconductor device makes it possible that the second interconnection connected to the opposed electrode is formed simultaneously with the first interconnection connected to the first pillar-shaped conductor.
In the above-described method for fabricating a semiconductor device, it is preferable that the first opening is an interconnection groove for burying the interconnection in the second insulation film. This fabrication of the semiconductor device makes it possible that the first interconnection is a buried interconnection buried in the second insulation film.
In the above-described method for fabricating a semiconductor device, it is preferable that the method further comprises after the first insulation film forming step: a sidewall film removing step of removing the sidewall film and forming a cavity between the first insulation film and the first pillar-shaped conductor. This fabrication of the semiconductor device makes it possible that the cavity is formed in a peripheral part of the first pillar-shaped conductor. This reduce parasitic capacitance between the interconnections.